Input devices, such as microphones or other devices providing an analog signal sensitive to introduced noise, relying on an applied bias voltage may face electromagnetic compatibility problems. Also noise components in the supply voltage may introduce noise. High currents to other parts of a device may give rise to voltage fluctuations, which in the case of microphones, can be discovered in the microphone signal as for example low frequency noise, often called “bumble bee” sound. These effects normally have to be dealt with by well-balanced designs of how wires and components are positioned and circuitry and signal processing for attenuating known noise. U.S. Pat. No. 6,978,029 B1 discloses a condenser microphone apparatus which is used for a radio apparatus and adapted to reduce noise due to radiation of a high frequency signal of a transmitting unit. A series resistor is provided between a drain and a source of an field effect transistor and a microphone output transmission line to prevent a high frequency voltage from being increased due to resonance of a bypass capacitor and microphone transmission line.
However, there is a desire to provide an alternative approach to reduce these interfering effects at an input of a signal amplifier receiving the signal from the analog device.